Cell-proliferation inhibiting VPg proteins, fragments or analogs thereof and their applications

ABSTRACT

Use of VPg proteins, fragments or analogs thereof having the ability to bind an eukaryotic initiation factor eIF4E, for inhibiting cell-proliferation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application filed under 35 U.S.C. 371 of International Application No. PCT/IB2008/002594, filed Jun. 13, 2008, which claims priority from European Application No. 07290740.5, filed Jun. 13, 2007.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to the field of cell proliferation-inhibiting proteins. More particularly, the invention relates to a protein comprising or consisting of a VPg protein, fragments thereof or analogs thereof, that are cytotoxic to eukaryotic cells, and/or inhibit the cell proliferation. The invention also relates to medical uses of such a protein, fragments thereof or analogs thereof.

Eukaryotic initiation factor eIF4E is a mRNA 5′ cap-binding protein, which both attaches mRNA and binds the eIF4G component of the eIF4F initiation complex. A significant fraction of eIF4E (up to nearly 70%) localizes to the nucleus (Lejbkowicz et al., 1992). It has been shown that nuclear eIF4E is involved in the nucleocytoplasmic transport of certain messenger RNAs (Lejbkowicz et al., 1992; Rosenwald et al., 1995; Rousseau et al., 1996; Lai and Borden, 2000). It has been demonstrated that the unchecked over-expression of eIF4E can cause cell growth and malignant transformation, whereas reduction of the eIF4E level can reverse the transformed phenotype (reviewed in Sonenberg and Gingras, 1998). Furthermore, in humans, some tumor types exhibit elevated levels of eIF4E (Ruggero and Pandolfi, 2003). It appears that at high eIF4E levels there is increased cytoplasmic level of proteins involved in the malignant transformation, due to the increase in the eIF4E-dependent transport of the appropriate mRNAs to the cytoplasm (Shantz and Pegg, 1994; Rousseau et al., 1996; Lai and Borden, 2000).

International Application No. WO 00/78803 describes eIF4E- binding peptides useful in therapy, and particularly for the induction of programmed cell death, presumably by disrupting the formation of the eIF4F complex. All these peptides comprise the amino acid sequence (motif) YxxxxLØ(SEQ ID NO: 31), wherein x is any amino acid and Ø is Leu, Met or Phe, required for binding human eIF4E (accession number NP_(—)001959 in the GENBANK database, Apr. 15, 2007 version).

Thus, there is an interest in the development of adequate eIF4E binding agents for use in anti-cancer therapy. There is also a need to find eIF4E binding agents possessing a distinct mechanism of action from that described above, to overcome drug resistances for instance.

Potato virus Y (PVY) is the type member of the Potyvirus genus, belonging to the Potyviridae family, the largest and economically most important group of plant viruses. Potyviruses have a so-called genome-linked VPg protein (hereinafter referred to as VPg protein or VPg) covalently attached to the 5′ end of their linear nucleic acid genomes (Riechmann et al., 1989 and Murphy et al., 1991). The potyvirus VPg protein is implicated in virus protein synthesis, long-distance movement in plant tissue and virus replication (Lellis et al., 2002; Schaad et al., 2002; Fellers et al., 1998). Early after potyvirus infection, the genomic RNA interacts with the host cellular machinery to initiate protein synthesis. The VPg protein seems to play an important role in this early event, because removal of VPg protein with proteinase K from the genomic RNA abolishes RNA infectivity and, in addition, decreases its translation efficiency in vitro (Leonard et al., 2000; Herbert et al., 1997). The amino acid sequence of the potato virus Y genome-linked protein VPg corresponds to the amino acid residues 336 to 523 of the amino acid sequence identified under accession number CAA82642 in the GENBANK database (Nov. 14, 2006 version). It is reproduced herein as SEQ ID NO: 2.

Recent studies have reported an interaction between the VPg protein of certain potyviruses (turnip mosaic virus, lettuce mosaic virus, tobacco vein mottling virus, potato virus Y) and the plant translation initiation factor eIF4E (Wittmann et al., 1997; Duprat et al., 2002; Kang et al., 2005; Grzela et al., 2006). It has also been shown that the VPg protein encoded by certain vertebrate viruses of the Caliciviridae family, such as the feline calcivirus (FCV), the lordsdale virus (LDV)) or the recently discovered murine norovirus (MNV-1) interact with the cap-binding protein eIF4E (Goodfellow et al., 2005; Chaudhry et al., 2006).

Grzela et al. (2006) have found that the interaction between PVY VPg protein and eIF4E seems to have rather low species specificity since it was also observed with yeast as well as with the insect (S. frigiperda) eIF4Es. The authors have also described that the VPg/eIF4E interaction results in some inhibition of cell-free protein synthesis in insect cells, but without leading to insect cell death. However, the PVY VPg primary amino acid sequence does not exhibit the eIF4E-binding motif YxxxxLØ SEQ ID NO: 31) described above.

SUMMARY OF THE INVENTION

Now, the Inventors have observed that, in presence of potato virus Y VPg protein, the nuclear pool of eIF4E was dramatically depleted in human cells. Thus and surprisingly, the Inventors have shown that the VPg protein immobilizes human initiation factor eIF4E in the cytoplasm, which results, contrary to what was observed previously in insect cells, in the inhibition of cell proliferation, leading to cell death.

Therefore, in a first aspect, the present invention relates to an isolated and purified protein comprising or consisting of a VPg protein or a fragment thereof of at least 8 amino acids or an analog thereof:

(i) having the ability to bind an eukaryote initiation factor eIF4E, preferably a mammal initiation factor eIF4E and more preferably a human initiation factor eIF4E, and

(ii) said protein, fragment thereof or analog thereof not comprising the amino acid motif YxxxxLØ(SEQ ID NO: 31), wherein x is any amino acid, Y is tyrosine (Tyr), L is leucine (Leu) and Ø is leucine (Leu), methionine (Met) or phenylalanine (Phe), as a medicament, preferably as an anti-cancer agent, or for use in treating cancer, preferably glioma, melanoma or a colon or lung cancer, in which the cancer cells express, preferably over-express, the initiation factor eIF4E, in a subject.

A “subject” refers to a mammal, preferably a human.

The characterization of the binding (or interaction) of a protein, a fragment thereof or an analog thereof according to the present invention to an eukaryotic (e.g., insect), preferably a mammal and more preferably a human eIF4E can be performed by an ELISA-based binding assay as described in Grzela et al. (2006). Advantageously, the dissociation constant between said protein, fragment thereof or analog thereof and said eIF4E is between about 5 nM and about 450 nM. Dissociation constant (or affinity) measurements may be made using methods known to those skilled in the art, including using the method described in Grzela et al. (2006). Optionally, this characterization may be combined with the in vitro determination of the change in cellular localization of eIF4E (immobilization of eIF4E in the cytoplasm) in the presence of a protein, a fragment thereof or an analog thereof of the present invention, in eukaryotic, preferably mammal and more preferably human cells. By way of example, the in vitro determination of the change in cellular localization of eIF4E in the presence of a protein, a fragment thereof or an analog thereof of the present invention can be performed in insect cells (e.g., High Five (Trichoplusia ni) cells), since these cells are a good predictive model for said determination in human cells. This determination can be performed as in Examples 3 or 4 below.

The terms “protein” and “peptide” may be used interchangeably herein. They are well known in the art and refer to a polymeric form of amino acids of any length. The terms also refer to a protein or peptide comprising chemically or biochemically modified amino acids, as well as a protein or peptide having modified peptide backbones, e.g. a protein or peptide containing one or more modifications to L-amino acid side-chains (for example D-amino acids), or to the alpha-amino acid backbone.

A VPg protein, according to the present invention, refers usually to a virus-encoded protein covalently attached to the 5′ end of the linear nucleic genome of said virus (Riechmann et al., 1989 and Murphy et al., 1991), and also comprises according to the present invention:

-   -   an isolated plant virus-encoded VPg protein,     -   a recombinant VPg protein of a plant virus, or     -   a synthetic VPg protein of a plant virus.

Preferably, said VPg protein consists of about 188 to 193 amino acid residues and includes the amino acid motif KGK and NMYG (SEQ ID NO: 26).

In a preferred embodiment, the VPg protein is the potato virus Y-encoded VPg protein of SEQ ID NO: 2.

The term “plant virus” refers to a virus capable of spreading through a plant and particularly of infecting at least one type of plant cells.

In another embodiment of the present invention, the VPg protein analog is an analog of PVY VPg protein of SEQ ID NO: 2, exhibiting at least 20%, and by order of increasing preference, at least 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or 99% sequence identity, or at least 45%, and by order of increasing preference, at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or 99% sequence similarity with the full-length of PVY VPg protein of SEQ ID NO: 2, provided that said VPg protein analog still has the ability to bind an eukaryote (e.g., insect) initiation factor eIF4E, preferably a mammal initiation factor eIF4E and more preferably a human initiation factor eIF4E as described above.

Examples of VPg protein analogs are VPg proteins encoded:

-   -   by other plant virus than the PVY, preferably belonging to the         Potyviridae family, more preferably to the Potyvirus genus, such         as the tobacco etch virus (TEV) (SEQ ID NO: 4), the clover         yellow vein virus (C1YVV) (accession number NP_(—)734169.1 in         the GENBANK database, Mar. 30, 2006, version, reproduced herein         as SEQ ID NO: 6), the tobacco vein mottling virus (TVMV)         (accession number NP_(—)734333.1 in the GENBANK database, Mar.         30, 2006, version, reproduced herein as SEQ ID NO: 8), the         turnip mosaic virus (TuMV) (SEQ ID NO: 10), the lettuce mosaic         virus (LMV) (accession number NP_(—)734159.1 in the GENBANK         database, Mar. 30, 2006, version, reproduced herein as SEQ ID         NO: 12), or     -   by a virus belonging to the Calcivirus family, preferably to the         Norovirus genus, such as the feline calicivirus (FCV) (accession         number Q66914 in the UniProtKB/Swiss-Prot database, reproduced         herein as SEQ ID NO: 27), human norovirus (HuNoV, accession         numbers P54634 in the UniProtKB/Swiss-Prot database, and         NP_(—)056820 in the GENBANK database, reproduced herein as SEQ         ID NO: 28 and 29 respectively) and murine norovirus (MNV)         (accession number YP_(—)720001 in the GENBANK database,         reproduced herein as SEQ ID NO: 30).

According to another embodiment of the present invention, the fragment of a protein as defined above is a fragment of a VPg protein or a fragment of a protein analog of a VPg protein as defined here above, comprising or consisting of at least 8, and by order of increasing preference at least 10, 15, 20, 25, 26 or 42 contiguous amino acids residues of said VPg protein or said analog thereof, but that retains the ability to bind an eukaryote (e.g., insect) initiation factor eIF4E, preferably a mammal initiation factor eIF4E and more preferably a human initiation factor eIF4E, as described above.

By way of example, the fragment as defined above comprises or consists of at least 8, and by order of increasing preference at least 10, 15, 20, 25, 26 or 42 contiguous amino acids residues of the amino acid sequence of any of the VPg protein as defined here above, preferably of SEQ ID NO: 2, 4, 6, 8, 10 or 12.

In another preferred embodiment of the present invention, the fragment of PVY VPg (SEQ ID NO: 2) comprises or consists of the amino acid sequence located:

-   -   between the arginine (Arg) at position 41 and the arginine (Arg)         at position 94 (also named VPg2; SEQ ID NO: 14) of SEQ ID NO: 2,         or     -   between the arginine (Arg) at position 41 and the glycine (Gly)         at position 82 (also named VPg4; SEQ ID NO: 16) of SEQ ID NO: 2,     -   between the arginine (Arg) at position 41 and the phenylalanine         (Phe) at position 66 (also named VPg5; SEQ ID NO: 18) of SEQ ID         NO: 2,     -   between the arginine (Arg) at position 41 and the arginine (Arg)         at position 59 (also named VPg1; SEQ ID NO: 20) of SEQ ID NO: 2,         or     -   between the phenylalanine (Phe) at position 60 and the arginine         (Arg) at position 94 (also named VPg3; SEQ ID NO: 22) of SEQ ID         NO: 2.

In another embodiment, the fragment comprises or consists of at least 8, and by order of increasing preference at least 10, 15, 20, 25 or 26 contiguous amino acids residues of the amino acid sequence SEQ ID NO: 16.

In another embodiment, the fragment of the VPg protein consists of an analog of SEQ ID NO: 16 exhibiting at least 60%, and by order of increasing preference, at least 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or 99% sequence identity, or at least 80%, and by order of increasing preference, at least 85%, 90%, 95%, 98% or 99% sequence similarity with the full-length of amino acid sequence of SEQ ID NO: 16.

In another embodiment, the fragment of the VPg protein consists of an analog of SEQ ID NO: 18 exhibiting at least 60%, and by order of increasing preference, at least 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98% or 99% sequence identity, or at least 80%, and by order of increasing preference, at least 85%, 90%, 95%, 98% or 99% sequence similarity with the full-length of amino acid sequence of SEQ ID NO: 18.

The term “analog” is intended to encompass any form of PVY VPg protein (SEQ ID NO: 2) or a fragment thereof (e.g., SEQ ID NO: 16 or SEQ ID NO: 18) as defined here above, wherein one or more of the amino acids within the amino acid sequence has been replaced with an alternative amino acid or another residue such as a carbohydrate, a lipid or a chemical and/or wherein one or more of the amino acids has been deleted or wherein one or more additional amino acids or another residue such as a carbohydrate, a lipid or a chemical has been added to the peptide chain or amino acid sequences of PVY VPg protein or a fragment thereof, provided that said analog still has the ability to bind an eukaryote (e.g., insect) initiation factor eIF4E, preferably a mammal initiation factor eIF4E and more preferably a human initiation factor eIF4E, as described above.

Many suitable computer programs for calculating the “identity” between two amino acid sequences are generally known in the art, such as BLAST program, choosing the scoring matrix BLOSUM62.

The term “similarity” refers to a comparison of the amino acid residues of two peptides wherein conservative amino acid residue substitutions are permitted, i.e. amino acid residues that share the same charge and the same polarity are considered similar. The conservative changes do not significantly alter the binding characteristics of the resulting peptide. The following is one example of various groupings of amino acids:

-   Amino Acids with Nonpolar R Group -   Alanine, Valine, Leucine, Isoleucine, Proline, Plenylalanine,     Tryptophan, Methionine. -   Amino Acids with Uncharged Polar R Groups -   Glycine, Serine, Threonine, Cysteine, Tyrosine, Asparagine,     Glutamine. -   Amino Acids with Charged Polar R Groups (Negatively Charged at pH     6.0) -   Asapartic acid, Glutamic acid -   Basic Amino Acids (Positively Charged at pH 6.0) -   Lysine, Arginine, Histidine (at pH 6.0) -   Amino Acids with OH Group -   Serine, Threonine, Tyrosine -   Amino Acids with an Aromatic Group -   Phenylalanine, Tyrosine, Tryptophan -   Another grouping may be according to molecular weight (i.e., size of     R groups):

Glycine 75 Alanine 89 Serine 105 Proline 115 Valine 117 Threonine 119 Cysteine 121 Leucine 131 Isoleucine 131 Asaparagine 132 Aspartic acid 133 Glutamine 146 Lysine 146 Glutamic acid 147 Methionine 149 Histidine (at pH 6.0) 155 Phenylalanine 165 Arginine 174 Tyrosine 181 Tryptophan 204

Particularly preferred conservative substitutions are:

-   -   Lysine for Arginine and vice versa such that a positive charge         may be maintained;     -   Glutamic acid for Aspartic acid and vice versa such that a         negative charge may be maintained;     -   Serine for Threonine such that a free —OH can be maintained;     -   Tyrosine for Phenylalanine such that the aromatic character of         the residue can be maintained; and     -   Glutamine for Asparagine such that a free —NH₂ can be         maintained.

The sequence similarity values provided herein are determined as described above in reference to calculation of sequence identity.

Optionally, the protein, fragment thereof or analog thereof as defined here above may comprise an amino acid sequence facilitating cellular uptake. Such amino acid sequences, known as Cell Penetrating Peptides, are well known in the art; See CELL PENETRATING PEPTIDES: PROCESSES AND APPLICATIONS, edited by Ulo Langel (2002); or Advanced Drug Delivery Reviews, 2005, 57:489-660). These include the Human Immunodeficency Virus type 1 (HIV-1) protein Tat or fragment thereof (Ruben et al., 1989), the herpes virus tegument protein VP22 (Elliott and O'Hare, 1997), penetratin (Derossi et al., 1996), protegrin 1 anti-microbial peptide SynB (Kokryakov et al., 1993) and the basic fibroblast growth factor (Jans, 1994).

A second aspect of the present invention relates to the use of a protein, a fragment thereof or an analog thereof as defined here above for the manufacture of a medicament for treating cancer, preferably glioma, melanoma or a lung or colon cancer, in which the initiation factor eIF4E is expressed or over-expressed, in a subject.

In a third aspect, the present invention provides an isolated nucleic acid sequence encoding a protein, a fragment thereof or an analog thereof as defined above. The nucleic acid sequence of the invention can be synthesized using standard techniques. Techniques for nucleic acid manipulation are known in the art (See, for example, in Sambrook J. et al. (2000) Molecular Cloning: A Laboratory Manual). By way of example, the nucleic acid sequence comprises or consists of the nucleic acid sequences SEQ ID NO: 1 (residues 1007 to 1570 of the nucleotide sequence identified under accession number Z29526 in the GENBANK database (Nov. 14, 2006 version) encoding PVY VPg protein), or SEQ ID NO: 3, 5, 7, 9, 11, 13, 15, 17, 19 or 21.

The present invention also provides a recombinant vector for the expression of a protein, a fragment thereof or an analog thereof as defined above. The recombinant vector comprises at least one nucleic acid sequence encoding a protein, a fragment thereof or an analog thereof as defined above, operably linked to at least one regulatory sequence.

The term “vector” is intended to mean a nucleic acid molecule capable of transporting another nucleic acid. By way of example, a vector which can be used in the present invention includes, but is not limited to, a viral vector (e.g., retrovirus, adenovirus, baculovirus), a plasmid, a RNA vector or a linear or circular DNA or RNA molecule which may consist of a chromosomal, non chromosomal, semi-synthetic or synthetic nucleic acid. Large numbers of suitable vectors are known to those of skill in the art and commercially available. Preferred vectors are those capable of autonomous replication (episomal vector) and/or expression of nucleic acids to which they are operably linked (expression vectors).

The term “operably linked” is intended to mean that the nucleotide sequence is linked to a regulatory sequence in a manner which allows expression of the nucleotide sequence.

The term “regulatory sequence” includes promoters, enhancers and transcriptional or translational control elements. Such regulatory sequences are also known in the art.

By way of example, expression vectors may include an origin of replication or autonomously replicating sequence (ARS) and expression control sequences, a promoter, an enhancer and necessary processing information sites, such as ribosome-binding sites, RNA splice sites, polyadenylation sites, transcriptional and translational terminator sequences, and mRNA stabilizing sequences. Such vectors may be prepared by means of standard recombinant techniques well known in the art and discussed, for example, in Sambrook et al., 2000.

The present invention also relates to the use of at least one recombinant vector expressing a nucleic acid encoding a protein, a fragment thereof or an analog thereof as defined above, for the preparation of a medicament for preventing or treating cancer.

The expression vector according to the present invention can also be used to transfect or transduct (e.g., by electroporation) or infect cells to thereby introduce or produce a protein, a fragment thereof or an analog thereof as defined above.

The present invention further relates to a host cell transfected to express a protein, a fragment thereof or an analog thereof as defined above. The host cell can be transfected with the nucleic acid or the vector of the present invention. The host cell may be any procaryotic or eucaryotic cell. For example, a protein, a fragment thereof or an analog thereof as defined above may be expressed in bacterial cells such as E. coli, insect cells, yeast, mammalian cells such as Chinese hamster ovary cells (CHO) or animal or human cells such as B16, LGL26, HeLa or 293 or any transformed cell line.

In another aspect, the present invention provides a pharmaceutical composition comprising a protein, a fragment thereof or an analog thereof or a recombinant vector as defined here above and a pharmaceutically acceptable carrier. The composition according to the present invention is useful for treating cancer, preferably glioma, melanoma or a colon or lung cancer, in which the initiation factor eIF4E is expressed or over-expressed, in a subject.

As used herein, “pharmaceutically acceptable carrier” is intended to include any and all solvents, dispersion media, liposomes, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. Suitable carriers are described in the most recent edition of Remington's Pharmaceutical Sciences, a standard reference text in the field. Preferred examples of such carriers or diluents include, but are not limited to, water, saline, Ringer's solutions, dextrose solution, and 5% human serum albumin. Cationic lipids, non-aqueous vehicles such as fixed oils and commercially available transductants may also be used. The use of such media and agents for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with a protein, a fragment thereof or an analog thereof as defined hereabove, use thereof in the composition of the present invention is contemplated.

By way of example, when the pharmaceutical composition comprises a protein, a fragment thereof or an analog thereof, then the pharmaceutically acceptable carrier is preferably a cationic lipid, or a mixture of non-cationic lipids and a cationic lipid.

In yet another aspect, the present invention comprises a method of inhibiting cancer cell proliferation, characterized in that said method comprises the step of treating a subject in need thereof with a composition comprising a protein, a fragment thereof or an analog thereof as defined here above.

The term “inhibiting” refers to slowing, decreasing, delaying, preventing or abolishing cell proliferation.

The term “cell proliferation” refers to the rate at which a group of cells divides. The number of cells growing can be easily quantified by one skilled in the art.

The term “cancer” refers to any of a number of diseases that are characterized by uncontrolled, abnormal proliferation of cells, the ability of affected cells to spread locally or through the bloodstream and lymphatic system to other parts of the body (i.e., metastases), as well as any of a number of characteristic structural and/or molecular features. Examples of cancers are breast, colorectal, liver, lung (such as small cells, non-small cells), bronchic, prostate, ovarian, brain, pancreatic, colon, head and neck, stomach and bladder cancers, non-Hodgkin's lymphomas, melanomas, leukaemias, neuroblastomas, gliomas, or glioblastomas.

A “cancer cell” is understood as a cell having specific structural properties, which can lack differentiation and be capable of invasion and metastasis. Preferably, the cancer cells express or over-express the initiation factor eIF4E. Cancer cells expressing eIF4E can be identified by methods known in the art, e.g., by DNA sequencing, or by Northern blot, or by immunochemistry using anti-eIF4E antibodies.

The term “over-express” means that the gene encoding eIF4E protein is expressed at a higher level compared to the one of a normal (i.e., non cancer cell) quiescent eukaryotic, mammal or human cell, resulting in the production in a cancer cell with eIF4E level exceeding the one normally produced in said normal cell. The normal range of expression or production can be determined by routine methods as by assaying the eIF4E protein, its mRNA, or its gene.

The term “treating” includes the administration of the protein, a fragment thereof or an analog thereof as defined here above, or a composition of the present invention, to a patient who has a disease or disorder (e.g., cancer or metastatic cancer), a symptom of disease or disorder or a predisposition toward a disease or disorder, with the purpose to cure, heal, alleviate, relieve, alter, remedy, ameliorate, improve or affect the disease or disorder, the symptoms of the disease or disorder, or the predisposition toward disease, or extend duration of life.

In another aspect, the present invention relates to the use of an isolated and purified initiation factor eIF4E, preferably from human origin, to screen for compounds (e.g., drugs) that mimic the binding specificity of a VPg protein, preferably the VPg protein of SEQ ID NO: 2, with eIF4E.

In another aspect the present invention relates to a method of screening for compounds (e.g., drugs) which mimic the binding specificity of a VPg protein, preferably of SEQ ID NO: 2, 4, 6, 8, 10 or 12, and more preferably of SEQ ID NO: 2, with the initiation factor eIF4E (preferably the human eIF4E), comprising the steps of i) contacting an isolated and purified eIF4E with a candidate compound and a protein, a fragment thereof or an analog thereof according to the present invention (e.g., SEQ ID NO: 2) and ii) detecting if this candidate compound inhibits the binding (or interaction) between eIF4E and said protein, a fragment thereof or an analog thereof. Standard methods are available in the art to carry out competitive binding assays. In addition, the detection of the binding (or interaction) of a peptide compound with eIF4E can be carried out as described in Grzela et al. (2006).

Candidate compounds include peptides such as soluble peptides, lipids, carbohydrates, lipopeptides, glycopeptides, and small organic and inorganic molecules.

The Table 1 below sums up the nucleic acid and peptide sequences used in the present description.

SEQ ID NO: Description of the sequence 1 nucleic acid sequence encoding PVY VPg protein 2 PVY VPg protein 3 nucleic acid sequence encoding TEV VPg protein 4 TEV VPg protein 5 nucleic acid sequence encoding ClYVV VPg protein 6 ClYVV VPg protein 7 nucleic acid sequence encoding TVMV VPg protein 8 TVMV VPg protein 9 nucleic acid sequence encoding TuMV VPg protein 10 TuMV VPg protein 11 nucleic acid sequence encoding LMV VPg protein 12 LMV VPg protein 13 nucleic acid sequence encoding VPg2 14 VPg2: amino acid sequence located between the arginine (Arg) at position 41 and the arginine (Arg) at position 94 of SEQ ID NO: 2 15 nucleic acid sequence encoding VPg4 16 VPg4: amino acid sequence located between the arginine (Arg) at position 41 and the glycine (Gly) at position 82 of SEQ ID NO: 2 17 nucleic acid sequence encoding VPg5 18 VPg5: amino acid sequence located between the arginine (Arg) at position 41 and the phenylalanine (Phe) at position 66 of SEQ ID NO: 2 19 nucleic acid sequence encoding VPg1 20 VPg1: amino acid sequence located between the arginine (Arg) at position 41 and the arginine (Arg) at position 59 of SEQ ID NO: 2 21 nucleic acid sequence encoding VPg3 22 VPg3: amino acid sequence located between the phenyl- alanine (Phe) at position 60 and the arginine (Arg) at position 94 of SEQ ID NO: 2 23 PVY VPg gene forward primer 24 PVY VPg gene reverse primer 25 polyhedrin promotor of AcMNPV 26 VPg motif NMYG 27 FCV VPg protein 28 HuNoV VPg protein 29 HuNoV VPg protein 30 MNV VPg protein 31 YxxxxL∅ peptide motif

BRIEF DESCRIPTION OF THE DRAWINGS

In addition to the preceding features, the invention further comprises other features which will emerge from the following description, which refers to examples illustrating the present invention, as well as to the appended figures.

FIG. 1: Interaction assay between human eIF4E and PVY VPg protein or fragments thereof (VPg1 to VPg4).

FIG. 2: Effect of VPg protein (SEQ ID NO: 2) expression on localization of native elF4E in insect cells. VPg was expressed in insect cells and distribution of native elF4E (left column) and recombinant VPg (VP column) was analyzed by confocal microscopy at the indicated timepoints post infection. The blow-ups of some cells are shown in the right column.

FIG. 3: Cytoplasmic retention of native elF4E is specific to VPg protein (SEQ ID NO: 2). Insect cells have been infected with bacmid (null baculovirus, left column), domain II of HCV helicase (middle column) and VPg (right column). Insect cells were analyzed by confocal microscopy at the indicated timepoints post infection.

FIG. 4: elF4E expression in fractionated insect cells. Insect cells infected at MOI 10 with appropriate baculoviruses were collected at indicated timepoints post infection, nuclei were separated from the cytoplasm and the subcellular extracts were analysed by SDS/PAGE and Western blot. The expression of the recombinant proteins is shown on the far right lower panel.

FIG. 5: Effect of PVY VPg protein on human eIF4E localisation. HeLa cells were transduced with VPg in the presence of Pro-Ject™ (purchased from Pierce) and analysed for presence of VPg and eIF4E by confocal miscroscopy (FIG. 1B). In FIG. 1A the HeLa cells were not transduced.

FIG. 6: Effect of PVY VPg protein on human cell proliferation. Cells were transduced with VPg using as protein transfer reagent TransPass P (Ozyme), and incubated for indicated periods. Cells damage was estimated using LDH Cytotoxicity detection assay (Clontech). The results show the average result obtained from three wells.

FIG. 7: Antitumour efficacy of PVY VPg protein in mice carrying GL26 (mouse glioma) tumours. 0=tumour volume measured at the beginning of the experiments. no treatment, 1=tumour volume measured 3 days later. Control=untreated mice. Buffer=mice electroporated with 0.9% NaCl. VPg=mice electroporated with 25 μg VPg in 0.9% NaCl. The same sign at the day 0 and 3 days later shows the volume of the tumour in the same mouse. The figure also give the fold increase in tumour size between time 0 and time 1 (fold 1 means no increase in tumour size).

FIG. 8: Antitumour efficacy of PVY VPg protein in mice carrying B16-ova (murine melanoma) tumours. B16-ova melanoma cells were injected into the thigh of the C57BL/6 mice (two groups of 8 animals). Two weeks later palpable tumors were formed. Control group was injected into the tumor with buffer mixed with Transpass P. Second group had injections of 50 micrograms of VPg transduced with Transpass P. every day for 6 days. The diameter of the tumours were measured every day during six days of treatment.

EXAMPLES Example 1 Materials and Methods

Cells.

High-Five insect (Trichoplusia ni) cells grown in suspension were cultured in Express Five SFM medium (Invitrogen) with gentamicin (50 mg/ml) and amphotericin B (0.25 mg/ml).

HeLa (human cervix carcinoma), B16-ova (mouse melanoma), GL26 (mouse glioma), IMR90 (human primary diploid fibroblasts) were grown in DMEM+GlutaMAX™-I (Gibco) medium complemented with 10% FCS.

Antibodies. Anti-his mouse monoclonal antibody (MMS-156P) was purchased from BabCO (Berkeley, Calif., USA). Anti-eIF4E mouse monoclonal (P-2; sc-9976) was from Santa Cruz Biotechnology (Santa Cruz, Calif., USA). It recognizes mouse, rat, human and porcine eIF4E. Anti-eIF4E rabbit polyclonal antibody against human eIF4E (purchased from Jackson ImmunoResearch Laboratories) was kind gift of Nahum Sonenberg (McGill University, Montreal Canada).

Anti-VPg rabbit polyclonal antibody was prepared in Elevage Scientifique des Dombes (Chatillon, France), using as antigen PVY hisVPg expressed in baculovirus (described below) and was affinity purified to VPg as follows. First an acetone powder obtained from 1 g of non-infected insect cells was used to remove cross-reacting antibodies from serum. Cell powder was added to the anti-VPg rabbit serum up to final concentration of 1%, and stored on ice overnight with gentle rolling. After centrifugation at 10 000 g for 10 min at 4° C., supernatant fraction was applied to CNBr-activated Sepharose 4B (purchased from Amersham Bioscience) containing VPg protein immobilized according to the manufacturers instructions. Bound antibody was eluted with 100 mM glycine pH 2.4 directly into tubes containing 30 μl of 3 M Tris, pH 8.8 and 20 μl 5 M NaCl.

Recombinant protein expression and purification. VPg gene of potato virus Y (strain O, accession number Z29526 in GENBANK database) was synthesized by PCR using plasmid pPVY15 (available under accession number Z29526 in GENBANK database, Nov. 14, 2006 version) as template, with the forward primer 5′ GGGGGGGATCCATGGGGAAAATAAA-3′ (SEQ ID NO: 23) and the reverse primer 5′ CCCCCAGATCTCTATTATTCATGCTCC-3′ (SEQ ID NO: 24, permitting the expression of the protein with the accession number CAA82642 in the GENBANK database. VPg cDNA was inserted into pFastBac HTb (purchased from Invitrogen, Carlsbad, Calif., USA) under the control of polyhedrin promotor (SEQ ID NO: 25) of AcMNPV (O'Reilly et al., 1992) and the recombinant baculovirus expressing his-tagged VPg was constructed using bacmid technology (purchased from Gibco BRL). The High Five (Trichoplusia ni) cells in suspension were infected with the recombinant baculovirus at MOI of 5 pfu/cells. Portion (100 ml) of recombinant baculovirus-infected HF cells was collected at 72 h p.i. suspended in 10 ml of 50 mM phosphate buffer, pH 7.0, containing 300 mM NaCl, 6 mM β-mercaptoethanol, 5% glycerol, 0.5% Tween 20 and protease inhibitor cocktail (Complete, purchased from Roche) and lysed by five cycles of freezing in liquid nitrogen and thawing at 37° C. After clearing the extract was passed by gravity through 1 ml of Ni-NTA agarose resin (purchased from Qiagen), equilibrated with 5 ml of lysis buffer. Bound proteins were eluted 5×500 μl of 250 mM imidazole in the 50 mM phosphate buffer, pH 7.0, containing 300 mM NaCl. Fusion tag was removed from VPg with TEV protease for 48 h incubation at 10° C. The resulting products were purified on 5 ml Hi-Trap Heparin column (purchased from Amersham Pharmacia). Proteins were applied on the column in 100 mM NaCl in 50 mM phosphate, pH 7.0, washed with the same buffer until the OD₂₈₀ reached stable level and then eluted in the gradient of NaCl in 50 mM phosphate, pH 7.0 (from 100 mM to 1 M). The fractions containing full-length hisVPg were collected, diluted and fractionated on 5 ml 15 S-Source column (purchased from Amersham Pharmacia) under conditions used for Hi-Trap Heparin column. His-tagged domain II of HCV helicase was expressed in HF cells after infection with the appropriate baculovirus at MOI 5 and purified as described (Boguszewska-Chachulska et al., 2004). All steps were analyzed on 12% SDS-PAGE by staining with CBB, using Precision Plus Protein Dual Colour (purchased from Bio-Rad) and BenchMark Prestained Protein Ladder (purchased from Invitrogen) as molecular weight standards.

Cell fractionation. High Five (T. ni) cells at the concentration 2×10⁶ cells/ml were infected with the baculoviruses expressing VPg protein or hisVPg, or domain II of HCV helicase or empty bacmid, at MOI 5. The infected cells were collected at the indicated times p.i. by centrifugations at 2000 rpm for 10 min. The pellets were washed twice in PBS and resuspended in four times the packed cell volume of hypotonic buffer (10 mM Tris, pH 7.9, 10 mM KCl, 3 mM DTT, 0.1 mM EDTA, 0.1 mM EGTA, 0.75 mM spermidine, 15 mM spermine). The cells were allowed to swell on ice for 30 min and checked with phase microscope for complete breakage. Then a 1/10 volume of restoration buffer (50 mM Tris, pH 7.9, 0.75 mM spermidine, 0.15 mM spermine, 10 mM KCl, 0.2 mM EDTA, 3 mM DTT, 67.7% sucrose) was added and the homogenate was layered over a 1 ml of sucrose cushion (30% sucrose in hypotonic buffer) and centrifuged in cold for 20 min at 3000 rpm. The pelleted nuclei were resuspended in four times the packed cell volume of nuclear extraction buffer (50 mM Tris, pH 7.5, 0.42 mM KCl, 6 mM DTT, 0.1 mM EDTA, 10% sucrose, 5 mM MgCl₂ 20% glycerol, 0.5 mM PMSF, 3 mg leupeptin per ml). The nuclei were then lysed by gentle rocking at 4° C. for 30 min at 4° C. Cytoplasmic and nuclear fractions were run on 15% SDS-PAGE followed by Western blot with anti-eIF4E antibody using ECL system with X-ray film. Densitometry of eIF4E bands was performed using GelDoc 2000 (purchased from BioRad) with Quantity One software.

Cell transduction with VPg protein. Transpass P (Ozyme) was combined with the purified VPg (0.1-2 μg/well) in 20 mM sodium phosphate, pH 7.0, containing 150 mM NaCl or in PBS according to the manufacturer instructions. Serum-free medium was added to the VPg/Transpass P mixture up to 250 μl final volume. HeLa cells (10⁵/well of 24-well dish) prewashed with serum-free medium were treated with such portion of delivery mixture. After indicated periods of incubation at 37° C. cells were used for studies on protein localization (confocal microscopy) and on proliferation (LDH Kit from Clontech).

Localization of elE4E and VPg in insect cells by confocal microscopy. High Five (T. ni) cells in suspension (2×10⁵ cells/ml) were infected with 10 MOI of baculoviruses expressing either hisVPg, or his-tagged domain II of HCV helicase or empty bacmid. Cells were collected at 48 h p.i by centrifugation at 3000 rpm, 5 min, 4° C., followed by two washes with 500 μl of PBS. Cells were fixed in cold 2% PFA, left for 10 min at RT, washed two times with 500 μl of PBS and resuspended in 300 μl of PBS. Portions of 100 μl of fixed cells were applied onto clean round coverslips and allowed to attach while drying in a lamina flow hood. Next day cover slips were put into wells of 24-wells plate and rehydrated at room temperature with 500 μl portions of PBS. After PBS removal, cells were permeabilized for 10 min with cold 0.1% Triton X-100 in PBS, rinsed twice with PBS and blocked with 5% serum in PBS for 30 min at RT. Alter 2 washes with PBS cells were incubated for 1 h at RT with primary antibodies (anti-his or anti-human elF4E) diluted 1/100 in PBS, followed by washing and 1 h incubation with secondary antibody (anti-rabbit FITC or anti-mouse Texas Red) (Jackson ImmunoResearch Laboratories) diluted 1:100 in PBS. Nuclei were stained with propidium iodide diluted in PBS (0.2-1 μg/ml). Alter three PBS rinses cover slips were mounted with 50% glycerol. Images were collected with BioRad MRC-600/Nikon Optiphot laser scanning confocal microscope.

Localization of eIF4E, VPg protein and PML in human cells by confocal microscopy. HeLa cells seeded on cover slips at about 60% confluency were washed 3 times with PBS and fixed in 2% cold PFA. Cells were infected with 10 MOI of baculoviruses expressing either hisVPg, or his-tagged domain 2 of HCV helicase or empty bacmid. Cells were collected at 48 h p.i by centrifugation at 3000 rpm, 5 min, 4° C., followed by two washes with 500 μl of PBS. Cells were fixed in cold 2% PFA, left for 10 min at Room Temperature, washed two times with 500 μl of PBS and resuspended in 300 μl of PBS. Portions of 100 μl of fixed cells were applied onto clean round coverslips and allowed to attach while drying in a lamina flow hood. Next day cover slips were put into wells of 24-wells plate and rehydrated min at room temperature with 500 μl portions of PBS. After PBS removal, cells were permeabilized for 10 min with cold 0.1% Triton X-100 in PBS, rinsed twice with PBS and blocked with 5% serum in PBS for 30 min at RT. After 2 washes with PBS cells were incubated for 1 h at room-temperature with primary antibodies (purified polyclonal anti-VPg, anti-eIF4E (MAb) and anti-PML (MAb) antibodies) diluted 1/100 in PBS, followed by washing and 1 h incubation with secondary antibody (anti-rabbit FITC or anti-mouse Texas Red) (purchased from Jackson ImmunoResearch Laboratories) diluted 1:100 in PBS. Nuclei were stained with propidium iodide diluted in PBS (0.2-1 μg/ml). After three PBS rinses cover slips were mounted with 50% glycerol. Images were collected with BioRad MRC-600/Nikon Optiphot laser scanning confocal microscope.

Effect of VPg protein on cell proliferation.

HeLa, B16, GL26 and IMR90 cells were seeded in 96-wells plate at 1×10⁴ cells per well and cultivated overnight. Portion of VPg (0.5-2 μg/well) was diluted into serum-free medium to obtain total volume 10 μl and incubated for 20 min with 0.2 μl TransPass P Protein Transfection Reagent (New England BioLabs) at room temperature. Cells were rinsed with serum-free medium and covered with 100 μl/well of mixture containing serum-free medium and transduction mix. After various time of incubation at 37° C. time the plates were centrifuged at 1000 rpm for 10 min and the supernatants were transferred to the new plate. The release of the malate dehydrogenase was measured with the LDH Cytotoxicity Detection Kit (Clontech), using multilabeled counter Victorl 412 (Wallac) at 490 nm. The level of cytotoxicity was calculated according to the LDH kit manual.

Example 2 In Vitro Interaction Assay of Human eIF4E with PVY VPg Protein and Fragments Thereof

Peptides SEQ ID NO: 2 (VPg), SEQ ID NO: 14 (VPg2), SEQ ID NO: 16 (VPg4), SEQ ID NO: 20 (VPg1), SEQ ID NO: 22 (VPg3) and SEQ ID NO: 18 (VPg5) were obtained by expression in E. coli as GST-fusion proteins. GST-fusion proteins were produced by standard methods from cDNA sequences (encoding VPg, VPg1, VPg2, VPg3, VPg4 or VPg5) cloned into vector pGEX-4T-1 (purchased from Amersham Biosciences).

ELISA technique was used for measuring the peptide's interaction with eIF4E immobilised in wells of 96-well dish. The interaction was monitored with an anti-GST antibody.

Human eIF4E, 100 ng in the coating buffer (0.1 M carbonate buffer, pH 9.6) was applied to 96-wells micro titer plate for overnight at 4° C. Excess eIF4E was removed and the wells were blocked with 5% milk in the PBST buffer for 1 h at 37° C. The plate was rinsed three times with PBST and incubated with increasing quantity of the various GST-fusions peptides in PBST, for 1 h at RT. After two PBST washes the incubation with anti-GST HRP-conjugated antibody (1:5000) (purchased from Amersham Biosciences) was carried out for 30 min at 37° C. After three PBST washes the reaction was developed with peroxides substrate and the absorbance was measured at 490 nm. Non-specific interactions of GST protein and anti-GST antibody with the GST-fusion peptides were substracted.

Results are shown in FIG. 1. Among the peptides tested, it appeared that SEQ ID NO: 22 (VPg3) is the weaker interactor. SEQ ID NO: 20 (VPg1) and SEQ ID NO: 14 (VPg2) showed approximately similar level of interaction, which is not far from VPg itself. The best eIF4E-interacting peptide seems to be SEQ ID NO: 16 (VPg4) and SEQ ID NO: 18 (VPg5), which, at higher concentration functions better than PVY VPg protein itself (SEQ ID NO: 2).

Example 3 In Vitro Cellular Localisation of eIF4E and PVY VPg Protein (SEQ ID NO: 2) in Insect Cells

Insect cells have been infected with baculovirus containing VPg gene of PVY (SEQ ID NO: 1). Confocal microscopy analysis revealed that the initiation factor eIF4E which localized at the beginning of infection in both compartiments, the nucleus and the cytoplasm (FIG. 2, 12 hpi), at 60 hpi timepoint was observed at the cell periphery (FIG. 2, left columns). VPg was observed only in the cytoplasm throughthout the infection (FIG. 2, VPg column). Merged images showed significant fraction of the elF4E in the nucleus at the beginning of infection but which diminished in the course of infection; at 24 hpi, the elF4E was visible in the cytoplasm and just at the nucleus periphery and at 60 hpi was observed in the cytoplasm only, showing significant overlap with the VPg.

To find out if the observed fluctuations in the elF4E localization are specifically due to the presence of VPg, it was investigated the localization of elF4E upon insect cells infection by baculovirus null (bacmid) which is a virus of origin, before insertion of the foreign gene, and also upon infection with baculovirus expressing non-relevant protein, the domain II of HCV helicase or VPg (FIG. 3). In non-infected insect cells elF4E was observed in both cellular compartments (the most upper panel). At 12 hpi cells infected with all three kinds of virus behaved similarly, whereas al 60 hpi only cells expressing VPg showed elF4E retention in the cytoplasm (FIG. 3, lowest panel). To obtain more quantitative data, the cell nucleus was separated from the cytoplasm, and elF4E quantity in both compartiments was assessed by Western blot (FIG. 4) followed by densitometry (Table 2 below).

TABLE 2 eIF4E distribution in insect cell cytoplasm and nucleus eIF4E in eIF4E in Hours p.i. baculovirus cytoplasm (%) nucleus (%) HF cells none 48.49 51.51 12 h bacmid 46.5 53.5 HCV helicase domain 51.54 48.46 VPg 55.5 44.5 hisVPg 53.45 46.55 24 h bacmid 57.83 42.17 HCV helicase domain 63.05 36.95 VPg 84.74 15.26 hisVPg 81.3 18.7 36 h bacmid 59.2 40.8 HCV helicase domain 62.5 37.5 VPg 87.1 12.9 hisVPg 83.33 16.67 48 h bacmid 55.99 44.01 HCV helicase domain 57.9 42.1 VPg 73.9 26.1 hisVPg 74.07 25.93

Cells infected with the baculovirus expressing his-tagged form of VPg were included in the experiment. In both non infected as well as cells infected for 12 h, comparable level of elF4E were present in the cytoplasm and the nucleus. The nuclear pool of the initiation factor diminished somewhat in the course of infection with bacmid and with helicase-expressing virus. However, upon expression of both VPg forms the nuclear pool of the elF4E was severely depleted; at 36 hpi the nuclear pool of elF4E accounted for 13% only of total cellular factor (down from 51-53%).

These experiments demonstrated that (1) VPg expressed alone in the baculovirus system remains in the cytoplasm; (2) in the presence of VPg, eIF4E is retained in the cytoplasm, resulting in the depletion of the initiation factor nuclear pool, but no inhibition of cell proliferation or cell death was observed probably because the insects cells contains several eIF4E isoforms.

Example 4 In Vitro Cellular Localization of eIF4E and PVY VPg Protein in Hela Cells

In order to know if VPg protein of plant virus is able to interact with human eIF4E, and resulting in the depletion of the nuclear pool of the initiation factor, several tranfection experiments were undertaken under various conditions. However, no cells expressing VPg could be recovered, suggesting toxic effect of VPg on human cells. Therefore the PVY VPg (SEQ ID NO: 2) was directly translocated into HeLa cell with Pro-Ject™ (purchased from Pierce), a cationic lipid mixture which allows intracellular delivery of proteins (see FIG. 5B). VPg was localized in the cytoplasm and affected strongly localization of native eIF4E. The initiation factor in control HeLa cells was observed in cytoplasm and nucleus. In the presence of VPg the level of eIF4E diminished significantly in the nucleus and overlapped to large extent with the cytoplasm-localized VPg.

Example 5 Effect of PVY VPg Protein on Cell Proliferation In Vitro

The LDH assay, which permits evaluation of cell damage was applied after VPg delivery to transformed cells, HeLa and B16 and to primary non-transformed human cells IMR90. Already 1 hour after VPg intracellular delivery both HeLa and B16 showed significant cell damage, Importantly, VPg introduced into primary IMR90 (human fetal lung fibroblasts) did not affect their growth (FIG. 6, IMR90).

The interaction of VPg with the eukaryotic initiation factor eIF4E results in the immobilization of the initation factor in the cytoplasm which leads to inhibition of cell growth followed by cell death. It is conceivable that the decrease of the eIF4E nuclear pool caused by interaction with VPg is accompanied by inhibition of the cytoplasmic transport of the messenger RNA of the pro-proliferative proteins, leading to the inhibition of cell growth with ensuing cell death.

Example 6 Efficacy of PVY VPg Protein on Cell Proliferation In Vivo

To study anticancer effect of PVY VPg protein (SEQ ID NO: 2), in vivo experiences have been undertaken. C57BL/6 mice were inoculated with GL26 cells inducing the mouse glioma tumours or with B16-ova melanoma cells.

GL26 tumours were established by injecting portions of 0.5×10⁶ GL26 cells in 100 μl foetal bovine serum into the right quadriceps of the adult female C57BL/6 mice. About two weeks later, during the exponential phase of glioma tumour growth, the VPg (25 μg in 0.9% NaCl) or 0.9% NaCl (50 μl) (buffer) were administered by electroporation to 2 groups of 5 mice, leaving the control group of mice untreated. VPg and buffer treated mice were anaesthetized by intraperitoneal injection of 250 μl of a solution containing 400 μl of Imalgen 1000, 2% Rompun (both from Centravet, Lapalisse, France) and 0.9% NaCl. Electroporation conditions were the following: 5×100 μsec pulses of the 800 volts from electro square porator T820 (BTX, San Diego, Calif., U.S.A), at 1 Hz frequency. The delay between pulses was one second. The animals were kept warm (37° C.) until they recovered from anaesthesia. The volume of the tumours was measured in mm³ every 2 or 3 days by slide calliper and compared with normally growing glioma tumors of the control untreated group of mice.

B16-ova melanoma tumours were established by injection of 5×10⁵ cells suspended in PBS into the left thighs of the C57BL/6 mice (two groups of 8 animals). After 12 days, when palpable tumors were formed, the tumours of the control group were injected with Transpass P mixed with the buffer. Second group had the injections of 50 micrograms of VPg transduced with Transpass P, every day for 6 days. The kinetics of tumour growth was followed by measuring every day the tumor diameter.

Results are shown in FIGS. 7 and 8. Administration of VPg slowed down or inhibited the growth of the tumours in comparison with control groups. This shows that VPg has indeed an inhibitory effect on tumour proliferation.

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1. A method of treating cancer in which the initiation factor eIF4E is expressed, in a subject in need thereof, comprising administering to said subject a therapeutically effective amount of a composition comprising an isolated and purified protein comprising or consisting of a VPg protein or fragment thereof having the ability to bind an eukaryotic intiation factor eIF4E, wherein the VPg protein or fragment thereof is selected from the group consisting of SEQ ID NO: 2, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, and SEQ ID NO:
 20. 2. The method according to claim 1, wherein the VPg protein or fragment thereof has the ability to bind a mammalian initiation factor eIF4E.
 3. The method according to claim 1, wherein the VPg protein or fragment thereof has the ability to bind a human initiation factor eIF4E.
 4. The method according to claim 1, wherein said composition comprises a purified protein comprising or consisting of the VPg protein of SEQ ID NO:
 2. 5. The method according to claim 1, wherein said composition comprises a purified protein comprising or consisting of the VPg protein fragment of SEQ ID NO:
 14. 6. The method according to claim 1, wherein said composition comprises a purified protein comprising or consisting of the VPg protein fragment of SEQ ID NO:
 16. 7. The method according to claim 1, wherein said composition comprises a purified protein comprising or consisting of the VPg protein fragment of SEQ ID NO:
 18. 8. The method according to claim 1, wherein said composition comprises a purified protein comprising or consisting of the VPg protein fragment of SEQ ID NO:
 20. 9. The method according to claim 1, wherein said cancer is a glioma, melanoma or a colon or lung cancer, in which the cancer cells express the initiation factor eIF4E.
 10. The method according to claim 1, wherein said cancer is a lung cancer. 